The invention concerns a remote control system for producing simple control operations, such as switching equipment on and off by means of a multiplicity of receivers, from a remote transmitter. The particular invention concerns the format of binary signal sequences transmitted with the receivers for selectively controlling one or more of them, each such sequence containing at least one control command, which includes an address for a single receiver, a group of receivers or all of them and control information for producing a controlled operation.
In such control systems, it is important to provide operation of the system that is to a very large extent free of interference of disturbance. This is particularly true in the case of commands transmitted by radio. It is particularly important to assure avoidance of producing an undesired initiation of false controlled operations by the wrong receiver or receivers as the result of disturbances or interference in the transmission path between transmitter and receiver. For this reason, error correcting codes with useful words and pseudowords are used for composing the control of messages. The useful words are distinguished by the use of a large number of binary places, which for maximum reliability is as large as possible, producing the so-called places-distance, the minimum of which is called the Hamming distance.
If the useful word radiated by the transmitter to the transmission path is disturbed, a pseudoword most commonly appears at the receivers. The receivers can thereby recognize the disturbance and remain inactive regarding the putative command to be performed. A large Hamming distance, however, means also an increased expense for decoding the control command at the receiver.
Publications hereby incorporated by reference:
1. (Regarding Nordstrom-Robinson coding.) PA1 F. J. Furrer PA1 Fehlerkorrigierende Block-Codierung Fuer Die PA1 Datenuebertragung PA1 Birkhaeuser-Verlag Basel, Seite 167 und Seite 243 PA1 2. (Regarding "Willard sequence") PA1 M. W. Willard PA1 Optimum Code Pattern for PCM Synchronization PA1 1962 National Telemetry Conference PA1 May 24, 1962 Washington, D.C. Vol. 1, Pages 1-9